The invention relates to a clamp for joining together a pair of flanges, the clamp having a multiple-link clamp chain and clamp shoes thereon and having wedge-shaped inner grooves, which straddle the edges of the flanges and press them against one another.
In clamps of this kind, the problem exists that at least some of the clamp shoes perform not only radial clamping movements but also movements in a radial-tangential direction during the closing process. In particular the clamp shoes situated nearest the clamp chain closure perform movements greatly deviating from the radial direction. In the final phase of the closing process, these movements are almost exclusively tangential in order to exert radially-directed clamping forces on the more remote shoes. During this last phase of the closing movement, therefore, the chain closing forces have to overcome the friction of the virtually tangential movements which contributes nothing to pressing the flanges together as well as produce the necessary radial flange pressing forces. A disadvantageous consequence of this is that very high pressing forces, which are necessary, for example, in the case of metal gaskets, cannot be brought to bear or can be applied only such that they are irregularly distributed over the circumference.
It is known from French Pat. No. 1,311,377 (FIGS. 11 and 12) to construct the clamp shoes in the form of wheels having a wedge-shaped circumferential groove. In this manner the sliding friction is replaced by a rolling friction. It is a great disadvantage, however, that the wheels make only a point or line contact with the edges of the flange and, at extremely high closing pressures, this leads to deformation of the flange edges. Such deformation interferes with the even rolling of the clamp shoes and thus with the even transmission of the clamping forces to the other shoes. The disadvantage of an uneven distribution of the pressure over the circumference of the flange is therefore not eliminated. In the subject matter of German Offenlegungsschrift No. 2,404,890, the longitudinal curvatures of the clamp elements is made greater than the curvatures of the flange itself. In this manner, greater bearing surfaces are created which are intended to eliminate deformation. Furthermore, the clamp links perfrom tilting and sliding movements during the closing process. The friction due to tangential sliding components of movement, which has to be overcome by the closing force, is therefore not as great, but it is nevertheless still present.